a) Field of the Invention
The present invention relates to a contact pin device for IC sockets and, more specifically, to a contact pin device which is to be used in an IC socket for electric transmission tests of an IC package having a plurality of connecting terminals on the package body and serves for connecting the IC socket to the connecting terminals.
b) Description of the Prior Art
IC sockets of this type are generally used for electrically connecting IC packages to external circuits, in particular, for carrying out various kinds of electric transmission tests of semiconductor integrated circuits built in the IC packages. Most of these IC sockets have connecting pins configured so as to correspond to the connecting terminals of various types of IC packages, for example, a BGA (Ball Grid Array) type IC package having nearly spherical connecting terminals, flat type IC package having gull-wing type connecting terminals (hereinafter referred to as gull-wing type), LGA (Land Grid Array) type IC package having pad-like connecting terminals, and LCC (Leadless Chip Carrier) type IC package.
Of the IC packages mentioned above, the BGA type IC package consists of a package body incorporating required circuits, and a large number of connecting terminals which are made of a solder material and arranged on a bottom surface of the package body in a matrix pattern spherically protruding for connection to external circuits. For electrically connecting the BGA type IC package to a printed circuit board, the package body is mounted at a predetermined location of the printed circuit board and the connecting terminals are connected directly to corresponding circuit terminals by partially melting the solder material of the connecting terminals.
Since the BGA type IC package has the connecting terminals which are to be soldered directly to the circuit terminals of the printed circuit board, this package may have gaps between the tips of the spherical connecting terminals and the circuit terminals after the package body is mounted at the predetermined location of the printed circuit board, thereby disabling soldering connection from making good electrical contact and constituting hindrance in practical works, in case where the tips of all the connecting terminals do not protrude downward in alignment, i.e., in case where the connecting terminals have protruding lengths which are different, though slightly, due to injury or breakage of any of the spherical tips.
The BGA type IC package, as well as the other types of IC packages, is subjected to various performance evaluation tests including a heat test referred to as burn-in test while electrically energizing all of the connecting terminals to thereby check whether or not the circuits operate as specified after manufacturing or before shipping. The IC socket is used for performing the performance evaluation tests of the IC package.
In FIGS. 1 and 2, a BGA type IC package A is composed of a package body 1 having required circuitry built therein, and a large number of connecting terminals 2 which are made of a solder material, protrude nearly spherically from a bottom surface 1a of the package body 1 and are arranged in a matrix pattern.
On the other hand, an IC socket B for the electric transmission tests of the IC package A consists of a socket body 11 having a concavity 12 formed at a predetermined location on a top surface of the socket body 11. Disposed in the concavity 12 is a floating plate 15 which is movably guided by guide pins 13 and always urged upward by springs 14.
Further, the floating plate 15 is formed with a positioning concavity 16 for receiving a lower section of the package body 1 while restricting a position thereof. Bored in the positioning concavity 16 are, at locations corresponding to the connecting terminals 2 of the package body 1, contact pin receivers 17 each of which has a tapered reception guide 17a as an upper half thereof and a space 17b as a lower half thereof.
Studded in the concavity 12 of the socket body 11, at locations corresponding to the contact pin receivers 17, are contact pins 21 which have contacts 21a having slightly larger diameters on their tops and are flexed in the spaces 17b so as to have required resilience. The contact pins 21 are inserted into the contact pin receivers 17 through the spaces 17b and kept in a condition where the contacts 21a protrude into the reception guides 17a by a required distance.
Though not illustrated in detail in FIGS. 1 and 2, the socket body 11 is provided with a cover pressing plate 18 which is hinged at one end thereof so that it can be opened and closed as desired, and can be sustained in an adequately latched condition at the other end to press down the package body 1 as uniformly as possible.
For testing the conventional IC package A by using the IC socket B, the lower section of the package body 1 is set and temporarily positioned in the positioning concavity 16 of the floating plate 15 by holding the cover pressing plate 18 open with respect to the socket body 11 and then the cover pressing plate 18 is kept in an adequately closed condition.
By the procedures described above, the floating plate 15 is pressed downward, against the resilience of the springs 14, under a pressure applied to the package body 1 by the cover pressing plate 18 and the contacts 21a of the contact pins 21 are brought into contact with the corresponding connecting terminals 2. In this condition, the contact pins 21 are flexed in the spaces 17b, as indicated by the dashed lines in FIG. 2, against the resilience of themselves, thereby producing the required contact pressure. The IC package A is thus set on the IC socket B as a preparation for performing the performance evaluation tests of the IC package A.
In the case of an ordinary IC socket of this type, however, good electrical connection may not be established between the contacts 21a of the contact pins 21 and the connecting terminals 2 since the IC socket cannot remove films of oxide or dust and foreign matters which are deposited on the surfaces of the contacts 21a and/or the connecting terminals 2 and hinder good electrical connection.
The IC socket B which is shown in FIGS. 1 and 2, by contrast, is configured so that strong resilience is imparted to the contact pins 21 and the contacts 21a of the contact pins 21 strongly press the surfaces of the connecting terminals 2, thereby breaking the films of oxide or pushing away the dust and foreign matters for establishing electrical connection securely.
In addition to the IC socket B described above which is configured so as to press the contacts 21a of the contact pins 21 strongly to the connecting terminals 2, there has been proposed another type of IC socket, for use with IC packages having the so-called gull-wing type connecting terminals, which is configured so as to establish secure electrical connection by strongly rubbing or wiping surfaces of the connecting terminals with contacts. A configuration of this IC socket is schematically shown in FIG. 3.
In FIG. 3, an IC package C has gull-wing type connecting terminals 24 which extend from both sides of a package body 23 outward and are then bent downward. Further, an IC socket D for electric transmission tests of the IC package C has a socket body 31 which has a concavity 32 formed at a predetermined location of a top surface thereof. Disposed in the concavity 32 is a floating plate 35 which is vertically guided by guide pin 33 and always urged upward by springs 34. Studded on edges of opposite sides of the concavity 32 of the socket body 31 are contact pins 41 which have tops configured as contacts 42 supported by springs 43 having a sideway-laid U-shape.
At a predetermined location of the upper surface of the floating plate 35, a positioning concavity 36 is formed which receives a lower section of the package body 23 of the IC package C having the connecting terminals 24 while restricting the position of the package body 23. The positioning concavity 36 is designed so that the connecting terminals 24 correspond to the contacts 42 of the contact pins 41 when the package body 23 is set in the positioning concavity 36. Further, the socket body 31 is provided with a cover pressing plate 37 which is to be used for pressing the package body 23 from upside as uniformly as possible and can be latched in a pressing condition thereof.
For mounting the IC package C having the conventional gull-wing type connecting terminals on the IC socket D, a lower section of the package body 23 is set and positioned in the positioning concavity 36 of the floating plate 35 with the cover pressing plate 37 open on the socket body 31, and then the cover pressing plate 37 is set an adequately closed condition. By the procedures described above, the connecting terminals 24 are brought into pressurized contact with the contacts 42 of the contact pins 41 under the pressure applied from the cover pressing plate 37 to the connecting terminals 24.
Since the springs 43 having the sideway-laid U-shape are pressed and urged in the process to bring the connecting terminals 24 into the pressurized contact with the contacts 42, contact surfaces of the connecting terminals 24 are rubbed or wiped with the contacts 42, whereby the films of oxide or dust and foreign matters are broken or removed for establishing secure electrical connection under a required contact pressure. After the IC package C has been set on the IC socket D, performance evaluation tests of the IC package C can be carried out as scheduled.
The wiping function obtained between the connecting terminals 24 and the contacts 42 is easily applicable, with the similar effect, also to an IC package E which, as shown in FIG. 4, has pad-like connecting terminals 46 located nearly flush with a bottom surface of an IC package body 45, through it is necessary to modify the shape of the contact pins shown in FIG. 3 so as to match with the pad-like connecting terminals 46.
However, the conventional IC socket B described above is disadvantageous in that it allows the surfaces of the connecting terminals 2 to be sunk or injured, thereby lowering a commercial value of the IC package when the surfaces of the connecting terminals 2 are strongly pressed by the contacts 21a of the contact pins 21.
When the burn-in test is effected for checking heat resistance of an IC package having the connecting terminals made of a solder material or the so-called solder balls in a condition where the connecting terminals 2 are connected to the contact pins 21, the solder material may be slightly softened by heat, whereby portions pressed by the contacts 21a are deformed and the deformed portions are hardened as they are after completing the performance evaluation tests. When the connecting terminals 2 are the solder balls as described above, marginal portions of the solder balls are brought into close contact with circuit terminals of a printed circuit board and partially melted for soldering the connecting terminals 2 to the circuit terminals. At this soldering stage, the deformed and hardened portions may be hardly melted. Similar defects may be produced when the connecting terminals 2 are not the solder balls, but made of a material having a relatively low melting point such as lead, zinc, aluminium, gold or silver. When the connecting terminals 2 have lower sections which are deformed or injured as described above, it is impossible to establish secure electrical connection between the connecting terminals and the circuit terminals of an IC package, in particular the BGA type IC package, at a stage in which the IC package is mounted on a printed circuit board.
Also in the case of the IC package C having the conventional gull-wing type connecting terminals or the IC package E having the pad-like connecting terminals, an area to be wiped with the contact of the contact pin is determined uniquely depending on an area of the connecting terminal to be brought into contact with the contact of the contact pin since the contact of the contact pin is urged linearly by a spring. As a result, the films of oxide may not be broken or dust may not be removed completely when a relatively narrow area of the connecting terminal is brought into contact with the contact, and the connecting terminal itself may be deformed in the case of the gull-wing type connecting terminal.
Even in a case where a relatively wide area of the connecting terminal is brought into contact with the contact of a contact pin 41, such as that shown in FIG. 3, a moving distance of the contact 42 is determined depending on a size of the spring 43. Accordingly, a similar problem is posed when the contact pin 41 has a relatively small spring 43 having the sideway-laid U-shape. An attempt which is made to enlarge the spring 43 will make it necessary to widen the socket body 31 on which the contact pins 41 are studded and such widening of the socket body 31 will reduce a number of IC sockets which can be mounted on a single printed circuit board to be tested, thereby resulting in lowering efficiencies in tests of IC packages.